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Thermoluminescence of LuPO4:0.1%Yb3+ sintered ceramics was investigated and simultaneous infrared 2F5/2 → 2F7/2 and UV-blue (YbCT3+)* → O2− charge transfer emissions of the Yb3+ impurity were observed around 150 °C (423 K) for the first time. Both photons were generated by one excited Yb3+*. LuPO4:Yb3+ was thus proved to be the first system showing the quantum cutting effect in thermoluminescence. Low concentration of the dopant was proved crucial to observe an intense CT emission at so high temperatures. These data revise deeply those reported previously on the thermal quenching of Yb3+ charge transfer luminescence in orthophosphates. In was formerly claimed that CT luminescence of Yb3+ in LuPO4 and similar hosts is quenched below 300 K. Similarly, the thermoluminescent emission of LuPO4:Yb3+ above room temperature was previously reported to appear only in the IR part of the spectrum around 980 nm. Our results fundamentally change this picture and prove that CT luminescence of Yb3+ in orthophosphates appears to be significant even above 150 °C (423 K). We demonstrate the great significance of the activator concentration in its CT luminescence thermal quenching. The Yb3+ impurity ion was found to act both as an electron trap and as a recombination center. Our data open the possibility to generate intense CT luminescence of Yb3+ in orthophosphates at room temperature and above which may make such phosphors rational for applications previously considered unattainable for them. [ABSTRACT FROM AUTHOR]

EPR spectroscopy in X- and Q-bands was employed to trace charge carrier trapping upon exposure to X-rays of LuPO4:Eu, LuPO4:Eu,Hf and YPO4:Eu,Hf flux-grown single crystals, as well as LuPO4:Eu sintered ceramics. These data were complemented with thermoluminescence (TL) studies on the same compositions. EPR spectra proved that all the single crystals contained Pb impurity incorporated from the flux. Upon exposure to X-rays the concentration of Pb3+ changed proving that Pb participated in carrier trapping. The ionizing radiation caused also partial conversion of Eu3+ into Eu2+ and in the (Eu,Hf) doubly doped crystals also Hf4+ was transformed into Hf3+ upon exposure to X-rays. In the LuPO4:Eu sintered ceramics X-rays transformed Eu3+ into Eu2+ and the strong EPR signal of a hole trapped at O2− in the vicinity of a defect (presumably Lu3+-vacancy) was recorded. Some contribution from the PO42− molecular ion could also be observed. However, in crystals the EPR signal from the latter was much more intense compared to the former. In ceramics, the trapped hole was found to hop between the O2− ions and only below ∼70 K it localized at just one of them. Complementary measurements of TL of the samples showed meaningful differences between the glow curves of the crystals and of the ceramics. The TL glow curve of the latter contained only one band peaking around 120 °C which is related to destruction of the trapped hole being mainly the O− center. All single crystals showed multi-peak TL glow curves covering the range of 30–500 °C. They were found to result mainly from a hole released from the PO42− molecular complex and to some extent also from the O− center. The results relative to EPR and TL spectroscopy proved that in orthophosphates Eu3+ is an effective electron trapping center while holes may be trapped at impurity ions, like Pb2+, or localized at oxygen ions possibly stabilized by nearby defects, e.g. Lu-vacancies. [ABSTRACT FROM AUTHOR]

Abstract: In this study, it is shown how the temperature range of luminescent thermometers can be widened in an unprecedented way by combining the intra‐ and interconfigurational transitions of the Pr3+ ion in a single material. Using Sr2GeO4:Pr3+ crystalline powders as an illustrative example, the implementation of luminescence thermometry is reported in the broadest temperature range up to now (17–600 K) with a remarkable performance: maximum relative sensitivity values of 9.0% · K−1 (at 22 K, cryogenic range), 0.6% · K−1 (at 300 K, physiological range), and 0.5% · K−1 (at 600 K, high‐temperature range) and minimum temperature uncertainty of 0.1 K. [ABSTRACT FROM AUTHOR]

Luminescence properties of SrS:Ce pellets sintered at 1700 °C were investigated under high pressure. Two different Ce3+-related emissions were confirmed to appear in the blue-green and red parts of the spectrum and were shown to shift significantly and linearly to longer wavelengths with increasing pressure. Changes in decay times of both emissions were also thoroughly analyzed. The results confirmed that Ce3+ ion pairing/clustering occurring due to their enhanced mobility at high temperatures is responsible for the appearance of the recently reported red Ce3+ emission in sintered SrS:Ce pellets. [ABSTRACT FROM AUTHOR]

Lu2O3:Eu phosphor fine powder with average size of crystallites of about 100-150 nm was synthesized. TEM images proved only an insignificant agglomeration of the phosphor. Using these fine particles and commercial polycarbonate a composite material was prepared in a form of 2 mm thick plate and its spectroscopic properties were compared to the powder. While the emission and luminescence excitation spectra were found very similar in both types of materials, the decay times of the Eu3+ red luminescence appeared to drop from 1.8-2 ms for the powder to 0.9-1 ms for the composite, with the latter value being perfectly the same as for the coarse-grained sintered translucent ceramics. Since the refractive indices of Lu2O3 host and the polycarbonate are 1.935 and 1.582, respectively, such a drastic change in the Eu3+ emission kinetics could not be fully explained by the variations of this parameter only. This result is with some disagreement with previously published data. POLYM. COMPOS., 37:1330-1334, 2016. © 2014 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]